test case fails

I just ran the Hello world module of the webshop. The simplest test case failed with error Error: expected "Content-Length" of "11", got "11". The complete error log mentioned below.

 Hello World
    1) should return hello world


  0 passing (24ms)
  1 failing

  1) Hello World
       should return hello world:
     Error: expected "Content-Length" of "11", got "11"
      at Test._assertHeader (D:\projects\techonology\node\koa\workshop\node_modules\supertest\lib\test.js:247:12)
      at Test._assertFunction (D:\projects\techonology\node\koa\workshop\node_modules\supertest\lib\test.js:281:11)
      at Test.assert (D:\projects\techonology\node\koa\workshop\node_modules\supertest\lib\test.js:171:18)
      at assert (D:\projects\techonology\node\koa\workshop\node_modules\supertest\lib\test.js:131:12)
      at D:\projects\techonology\node\koa\workshop\node_modules\supertest\lib\test.js:128:5
      at Test.Request.callback (D:\projects\techonology\node\koa\workshop\node_modules\superagent\lib\node\index.js:706:12)
      at IncomingMessage.parser (D:\projects\techonology\node\koa\workshop\node_modules\superagent\lib\node\index.js:906:18)
      at endReadableNT (_stream_readable.js:1101:12)
      at process._tickCallback (internal/process/next_tick.js:114:19)

Start by locating the Hello world module and its simplest test, then reproduce the reported supertest failure. Inspect the test and the response involved in the Content-Length assertion; done means the simplest test runs successfully with the expected header value.